Extendable Ears

From UnknowableWiki

Extendable Ears are flesh coloured strings which are used for listening to things from a distance. They were created by Fred and George Weasley for Weasleys' Wizard Wheezes, their joke empire, during the summer of 1995 (OP4). To use them, one inserts an end of the Extendable Ear into one's ear and says "Go", causing the other end to go where a conversation is taking place (OP23).